The conventional blow gun is used for removing dust by pressurized air flow, especially for those positions where the user's hand cannot reach such as positions in ducts, narrow spaces or high positions. The blow gun uses pressurized air to generate air flow to remove the dust from the positions mentioned above.
As shown in FIG. 7, the conventional blow gun 8 has a valve 81 and a spring 82 respectively connected to different axes of the blow gun 8. The valve 81 and the spring 82 respectively bias the top and bottom of the press rod 83 and are not located perpendicular to each other. The spring 82 easily reaches its fatigue point when the press rod 83 is operated for a period of time, and this causes leakage from the valve 81.
FIG. 8 shows Taiwanese Patent TW-M417959, wherein the blow gun 90 is connected with a source of pressurized air and the volume adjustable device 94 is exposed on the outside of the blow gun 90 and the volume of the pressurized air can be adjusted by rotating the knob 941 of the volume adjustable device 94. The knob 941 is connected with the valve blade 931 of the valve 93 so that the valve blade 931 is rotated between the first position and the second position. When the valve blade 931 is at the first position, the curved and concaved surface of the valve blade 931 seals the outlets 911, 921 to the inlet paths 91, 92, therefore, the pressurized air cannot enter into the path 95. When the valve blade 931 is at the second position, the valve blade 931 opens the outlets 911, 921. In other words, the valve blade 931 is in the closed position at the first position and in the open position at the second position. The valve blade 931 can also be positioned between the first and second positions to adjust the volume of the pressurized air.
Although the valve blade 931 can be positioned between the first and second positions to adjust the volume of the pressurized air, the opening of the trigger 96 cannot be controlled so that the trigger 96 may be unintentionally touched to action and this may result in dangerous situations.
The present invention intends to provide a volume adjustable device for a blow gun so as to adjust the volume of air passing through the blow gun.